Kubernetes provides a resource named ConfigMap to externalize the parameters to pass to your application in the form of key-value pairs or embedded application.properties|yaml files. The Spring Cloud Kubernetes Config project makes Kubernetes `ConfigMap`s available during application bootstrapping and triggers hot reloading of beans or Spring context when changes are detected on observed `ConfigMap`s.

The default behavior is to create a ConfigMapPropertySource based on a Kubernetes ConfigMap which has metadata.name of either the name of your Spring application (as defined by its spring.application.name property) or a custom name defined within the bootstrap.properties file under the following key spring.cloud.kubernetes.config.name.

However, more advanced configuration are possible where multiple ConfigMaps can be used This is made possible by the spring.cloud.kubernetes.config.sources list. For example one could define the following ConfigMaps

spring:
  application:
    name: cloud-k8s-app
  cloud:
    kubernetes:
      config:
        name: default-name
        namespace: default-namespace
        sources:
         # Spring Cloud Kubernetes will lookup a ConfigMap named c1 in namespace default-namespace
         - name: c1
         # Spring Cloud Kubernetes will lookup a ConfigMap named default-name in whatever namespace n2
         - namespace: n2
         # Spring Cloud Kubernetes will lookup a ConfigMap named c3 in namespace n3
         - namespace: n3
           name: c3

In the example above, it spring.cloud.kubernetes.config.namespace had not been set, then the ConfigMap named c1 would be looked up in the namespace that the application runs

Any matching ConfigMap that is found, will be processed as follows:

The single exception to the aforementioned flow is when the ConfigMap contains a single key that indicates the file is a YAML or Properties file. In that case the name of the key does NOT have to be application.yaml or application.properties (it can be anything) and the value of the property will be treated correctly. This features facilitates the use case where the ConfigMap was created using something like:

kubectl create configmap game-config --from-file=/path/to/app-config.yaml

Example:

Let’s assume that we have a Spring Boot application named demo that uses properties to read its thread pool configuration.

This can be externalized to config map in yaml format:

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  pool.size.core: 1
  pool.size.max: 16

Individual properties work fine for most cases but sometimes embedded yaml is more convenient. In this case we will use a single property named application.yaml to embed our yaml:

 ```yaml
kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  application.yaml: |-
    pool:
      size:
        core: 1
        max:16

The following also works:

 ```yaml
kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  custom-name.yaml: |-
    pool:
      size:
        core: 1
        max:16

Spring Boot applications can also be configured differently depending on active profiles which will be merged together when the ConfigMap is read. It is possible to provide different property values for different profiles using an application.properties|yaml property, specifying profile-specific values each in their own document (indicated by the --- sequence) as follows:

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  application.yml: |-
    greeting:
      message: Say Hello to the World
    farewell:
      message: Say Goodbye
    ---
    spring:
      profiles: development
    greeting:
      message: Say Hello to the Developers
    farewell:
      message: Say Goodbye to the Developers
    ---
    spring:
      profiles: production
    greeting:
      message: Say Hello to the Ops

In the above case, the configuration loaded into your Spring Application with the development profile will be:

  greeting:
    message: Say Hello to the Developers
  farewell:
    message: Say Goodbye to the Developers

whereas if the production profile is active, the configuration will be:

  greeting:
    message: Say Hello to the Ops
  farewell:
    message: Say Goodbye

If both profiles are active, the property which appears last within the configmap will overwrite preceding values.

To tell to Spring Boot which profile should be enabled at bootstrap, a system property can be passed to the Java command launching your Spring Boot application using an env variable that you will define with the OpenShift DeploymentConfig or Kubernetes ReplicationConfig resource file as follows:

apiVersion: v1
kind: DeploymentConfig
spec:
  replicas: 1
  ...
    spec:
      containers:
      - env:
        - name: JAVA_APP_DIR
          value: /deployments
        - name: JAVA_OPTIONS
          value: -Dspring.profiles.active=developer

Notes: - check the security configuration section, to access config maps from inside a pod you need to have the correct Kubernetes service accounts, roles and role bindings.

Another option for using ConfigMaps, is to mount them into the Pod running the Spring Cloud Kubernetes application and have Spring Cloud Kubernetes read them from the file system. This behavior is controlled by the spring.cloud.kubernetes.config.paths property and can be used in addition to or instead of the mechanism described earlier. Multiple (exact) file paths can be specified in spring.cloud.kubernetes.config.paths by using the , delimiter

Kubernetes has the notion of Secrets for storing sensitive data such as password, OAuth tokens, etc. This project provides integration with Secrets to make secrets accessible by Spring Boot applications. This feature can be explicitly enabled/disabled using the spring.cloud.kubernetes.secrets.enabled property.

The SecretsPropertySource when enabled will lookup Kubernetes for Secrets from the following sources:

Please note that by default, consuming Secrets via API (points 2 and 3 above) is not enabled for security reasons and it is recommended that containers share secrets via mounted volumes. If you enable consuming Secrets via API, then it is recommended access to Secrets is limited by an [authorization policy such as RBAC](https://kubernetes.io/docs/concepts/configuration/secret/#best-practices ).

If the secrets are found their data is made available to the application.

Example:

Let’s assume that we have a spring boot application named demo that uses properties to read its database configuration. We can create a Kubernetes secret using the following command:

oc create secret generic db-secret --from-literal=username=user --from-literal=password=p455w0rd

This would create the following secret (shown using oc get secrets db-secret -o yaml):

apiVersion: v1
data:
  password: cDQ1NXcwcmQ=
  username: dXNlcg==
kind: Secret
metadata:
  creationTimestamp: 2017-07-04T09:15:57Z
  name: db-secret
  namespace: default
  resourceVersion: "357496"
  selfLink: /api/v1/namespaces/default/secrets/db-secret
  uid: 63c89263-6099-11e7-b3da-76d6186905a8
type: Opaque

Note that the data contains Base64-encoded versions of the literal provided by the create command.

This secret can then be used by your application for example by exporting the secret’s value as environment variables:

apiVersion: v1
kind: Deployment
metadata:
  name: ${project.artifactId}
spec:
   template:
     spec:
       containers:
         - env:
            - name: DB_USERNAME
              valueFrom:
                 secretKeyRef:
                   name: db-secret
                   key: username
            - name: DB_PASSWORD
              valueFrom:
                 secretKeyRef:
                   name: db-secret
                   key: password

You can select the Secrets to consume in a number of ways:

Notes: - The property spring.cloud.kubernetes.secrets.labels behaves as defined by Map-based binding . - The property spring.cloud.kubernetes.secrets.paths behaves as defined by Collection-based binding . - Access to secrets via API may be restricted for security reasons, the preferred way is to mount secret to the POD.

Example of application using secrets (though it hasn’t been updated to use the new spring-cloud-kubernetes project): spring-boot-camel-config

Some applications may need to detect changes on external property sources and update their internal status to reflect the new configuration. The reload feature of Spring Cloud Kubernetes is able to trigger an application reload when a related ConfigMap or Secret changes.

This feature is disabled by default and can be enabled using the configuration property spring.cloud.kubernetes.reload.enabled=true (eg. in the application.properties file).

The following levels of reload are supported (property spring.cloud.kubernetes.reload.strategy): - refresh (default): only configuration beans annotated with @ConfigurationProperties or @RefreshScope are reloaded. This reload level leverages the refresh feature of Spring Cloud Context. - restart_context: the whole Spring ApplicationContext is gracefully restarted. Beans are recreated with the new configuration. - shutdown: the Spring ApplicationContext is shut down to activate a restart of the container. When using this level, make sure that the lifecycle of all non-daemon threads is bound to the ApplicationContext and that a replication controller or replica set is configured to restart the pod.

Example:

Assuming that the reload feature is enabled with default settings (refresh mode), the following bean will be refreshed when the config map changes:

@Configuration
@ConfigurationProperties(prefix = "bean")
public class MyConfig {

    private String message = "a message that can be changed live";

    // getter and setters

}

A way to see that changes effectively happen is creating another bean that prints the message periodically.

@Component
public class MyBean {

    @Autowired
    private MyConfig config;

    @Scheduled(fixedDelay = 5000)
    public void hello() {
        System.out.println("The message is: " + config.getMessage());
    }
}

The message printed by the application can be changed using a ConfigMap as follows:

apiVersion: v1
kind: ConfigMap
metadata:
  name: reload-example
data:
  application.properties: |-
    bean.message=Hello World!

Any change to the property named bean.message in the ConfigMap associated to the pod will be reflected in the output. More generally speaking, changes associated to properties prefixed with the value defined by the prefix field of the @ConfigurationProperties annotation will be detected and reflected in the application. [Associating a ConfigMap to a pod](#configmap-propertysource) is explained above.

The full example is available in [spring-cloud-kubernetes-reload-example](spring-cloud-kubernetes-examples/kubernetes-reload-example).

The reload feature supports two operating modes: - event (default): watches for changes in config maps or secrets using the Kubernetes API (web socket). Any event will produce a re-check on the configuration and a reload in case of changes. The view role on the service account is required in order to listen for config map changes. A higher level role (eg. edit) is required for secrets (secrets are not monitored by default). - polling: re-creates the configuration periodically from config maps and secrets to see if it has changed. The polling period can be configured using the property spring.cloud.kubernetes.reload.period and defaults to 15 seconds. It requires the same role as the monitored property source. This means, for example, that using polling on file mounted secret sources does not require particular privileges.

Notes: - Properties under spring.cloud.kubernetes.reload. should not be used in config maps or secrets: changing such properties at runtime may lead to unexpected results; - Deleting a property or the whole config map does not restore the original state of the beans when using the refresh level.